A central theme in our studies of primate social behavior at the Yerkes RPRC is reciprocal altruism. The reciprocity studies focus on food-sharing in capuchin monkeys (chimpanzees are also being studied under the general support of our chimpanzee project "Behavioral and Veterinary Approaches to Primate Breeding"). The capuchin study is of an experimental nature, in which one monkey of a pair receives food while separated from the other by mesh. The food possessor often shares with the other through the mesh. These monkeys live normally in a social group pairs are removed for brief test periods. After first having studied sharing behavior itself, and the degree to which it occurs reciprocally, the purpose of the current study is to investigate to what extent, if at all, food sharing is used by capuchins as a payment for cooperation. For reciprocal exchange to occur it would seem necessary that individuals not only assist conspecifics, but also take notice of received assist ance. The central question here is whether rewards obtained through cooperation are more readily shared than rewards obtained through individual effort. Pairs of monkeys will be presented with tasks in which one subject cannot obtain food unless assisted by the other. Food will be placed outside a test chamber on a tray too heavy for a single monkey to pull close. If both monkeys pull together, however, one of them will obtain food that subsequently can be shared with the other. Variations on this task, and control procedures will be performed as well. If cooperative efforts do indeed promote sharing, this would suggest that the principle of "one good turn deserves another" is not limited to our own species.